Principal Investigator Jennifer Rupp
Ionically-controlled memristors could allow for the realization of highly functional, low-energy circuit elements operating on multiple resistance states and to encode information beyond binary. The application of a sufficiently high electric field induces a non- volatile resistance change linked to locally induced redox processes in the oxide. State-of-the-art devices operate mainly on O2−, Ag+ or Cu2+ ions hopping over vacancies. Surprisingly, despite their fast diffusivity and stability towards high voltages, lithium solid-state oxide conductors have almost been neglected as switching materials. Work investigates lithium ionic carrier and defect kinetics in oxides to design material architectures and interfaces for novel Li-operated memristors as alternative memory material.
Extensive efforts were devoted to understand the growth of the chosen Li-oxides conductor thin films by Pulsed Laser Deposition (PLD) and to microfabricate model thin film architecture devices. In- house overlithiated pellets of the selected oxides were synthesized and used as PLD targets. Dense, crack-free thin film oxides have been successfully grown on Pt/Si3N4/ Si substrates, including multilayer heterostructures of two selected Li-oxide materials. Remarkably, Pt/Li- oxide/Pt structures show a significant bipolar resistive switching effect with a resistance ratio Roff/Ron~104-105 at beneficial low operation voltages to reduce the footprint at operation (~3V for a non-device lab optimized architecture).
In addition, sweep rate, thickness, and area dependence studies suggest that the bulk oxide plays a major role in the diffusion of the ionic species for achieving a large and tunable resistance ratio. This phenomenon makes the new investigated Li-oxides novel candidate material as new neuromorphic computing element. In situ Raman Spectroscopy and TEM experiments will shed light on the microstructure and its defects and will allow a better understanding of the underlying physical mechanism of the switching behavior. Also, new routes are explored to modify the lithiation degree of the thin films and would add an extra parameter to tune and alter switching kinetics and resistance retention.